Metalized stems for low-pressure discharge tubes



J. J. MASON Get. 19, 1954 METALIZED STEMS FOR LOW-PRESSURE DISCHARGE TUBES Filed March 28, 1951 INVENTOR J. J? M6 50 94% ATTORNEY Patented Oct. 19, 1954 METALIZED STEMS FORLOW-PRESSURE DISCHARGE TUBES Julien J. Mason, West Caldwell, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application March 28, 1951, Serial No. 217,943 2 Claims. (01. 313-109) This invention relates to stems and, more particularly, to metallized stems for fluorescent lamps and other low pressure discharge tubes of the positive column type.

An example of a low pressure discharge tube of the positive column type is the fluorescent lamp Which is essentially an electric discharge source consisting of a tubular envelope having electrodes sealed into each end and containing mercury vapor at low pressure and a small amount of an inert gas, such as argon, as an aid in starting. The inner walls of the envelope are coated with fluorescent powders which give off light when activated by ultraviolet energy radiated at 2537 A. U. When the proper volt age is impressed on the electrodes, a flow of electrons is driven from one electrode and attracted or pulled to the other. As these electrons speed through the tube, they collide with the mercury atoms, causing a state of excitation which produces the desired ultraviolet radiation. The fluorescent powders, commonly known as phosphors, absorb this invisible energy and radiate visible light.

During the half cycle of operation on alternating current in which one electrode of a fluorescent lamp is functioning as an anode, a deficiency of positive ions occurs near this electrode or anode and a negative space charge builds up thereabout. An anode voltage drop results from this space charge and is a measure of the energy which must be imparted to the electrons in order to overcome the repelling force of the space charge. Reducing the anode drop in a fluorescent lamp and consequently the power input increases the luminous efiiciency, namely lumens of light output per watt of power input. Ithas been found that to efficiently draw the required lamp current from the random electrons in the positive column and thus substantially minimize anode voltage drop a fairly large anode area of low work function material is required.

In the conventional lamp the discharge path is substantially limited to the region between the small electrodes which extend inwardly from each of the lamp, leaving some end darkness which impairs lamp appearance. If large anode structures are inserted into the lamp for the purpose of reducing the anode voltage drop, the brightness at the ends of the lamp will be further reduced, due to shielding and absorption by said anodes. By the means to be disclosed the anode drop can be reduced and this appearance defect can be alleviated by increasing the length of the discharge path and by reflecting from the lamp ends the radiations which otherwise would be absorbed therein.

Hence it has been found advantageous according to my invention to improve both lamp efliciency and lamp appearance by coating the outside surface of the electrode stems which are exposed to the lamp interior with a light reflecting film of a metal, such as aluminum,

and electrically connecting said coating to one I radiation which would otherwise be absorbed by the lamp stem and base. In addition, an evaporated aluminum coating provides gettering action for deleterious residual gases released from lamp parts during the operative life of the lamp.

In its general aspect the present invention has the object of overcoming the aforementioned disadvantages of the prior art fluorescent lamps.

Specifically, an object of the present invention is to provide on a stem for a lamp or tube a large anode area with a low Work function to reduce anode voltage drop.

Another and specific object is to provide on a stem for a lamp a large anode area to increase light output due to a longer discharge path to said anode.

Another object is to provide a reflecting surface for ultra-violet light which will reflect radiations normally lost therethrough.

An additional object is to provide on a stem for a lamp a reflecting surface for visible light which will reflect visible radiations which might otherwise be lost therethrough.

A further object is to provide a coating on a stern for a lamp or tube which will act as a getter for deleterious gases released by parts of said lamp or tube during operation.

Other objects and advantages of the invention will appear to those skilled in the art to which it appertains as the description proceeds, both by direct recitation and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views:

Fig. 1 is an elevational view of a fluorescent lamp with the fluorescent coating on the envelope broken away to show the filamentary electrode mounts at each end;

Fig. 2 is an elevational view of an electrode mount having the vitreous stem coated with a film of aluminum;

Fig. 3 is a sectional view of the vitreous stem of Fig. 2;

Fig. 4 is a sectional view of the stem along line IV--IV of Fig. 3;

Fig. 5 is a sectional view similar to Fig. 4 showing a method of amxing an electrical connector to the stem press prior to aluminizing.

Fig. 6 is a sectional view similar to Fig. 3., showing a modification of the method of electrically connecting an aluminum film on the stem to the filamentary electrode.

In Fig. l, the reference numeral Ill designates a tubular vitreous envelope of a fluorescent lamp H. While a fluorescent lamp has been selected as an embodiment of the present invention, it will be understood that the invention is not restricted to use with fluorescent lamps. This envelope is is coated on its inner surface wtiha fluorescent material l2 and has a filamentary electrode mount [3 sealed. into each end. Such amount comprises a stem l4, consisting. of a flare I5 and two leadingin conductors H5 sealed to said flare by means of a press and a filamentary electrode I! mounted on said conductors, as shown in Fig. 2.

It will be understood that in a conventional fluorescent lamp employed here as illustrative of a low pressure gaseous discharge tube of the positive column type that the filamentary electrode 1'! serves as cathode on one half cycle and as anode on the other half cycle of operation on an alter nating current system.

The flare i5 is a piece of tubing, commonly soft glass, having one end flared axially outwardly and having the sealing portions, suitably "Dumetf of. conductors l5 sealed through a press l8 at the other end. Dumet is the trade name for lead.- ing-in conductors comprising a chrome ironv core enclosed in a copper sheath having a total thickness approximately of the finished conductor diameter. One of the electrode mounts l3 has a suitabletubulation IQ for evacuating the envelope and the admission of argon and mercury during the exhaust of said lamp ll. After an exhaust which may consist of preliminary evacuation,

bake, electrode treating, mercury and argon fill, and tip off, bases 20 are affixed to the lamp. H at both ends of the envelope.

According to my invention, the outside, surface of each of the stems I4 is provided with a light reflecting metallic film, such asv aluminum 2 l, which is electrically connected to oneof the leading-in conductors [6 by a two piece metallic con nector 22, suitably Dumet and nickel- This connector 22 may be U-shaped in. configuration having one elongated side leg of Dumet for scaling to the press it! of stem Id and another leg 23 of nickel.

To prepare stem l4 for aluminizing, the elongated side leg 23 of connector 22 is covered with a thin bead of softglass, suitably the same as the stem glass, and is then partially embedded substantially along its length into the side wall of the press i 81, as shown in Fig. 5. The portions of the thinbead and the connector protruding from the side wall are ground, as by an abrasive wheel, flush with said side wall, thus exposing a reasonably large and firmly afljxed metallic surface of the connector upon whichevaporated' aluminummay be deposited. The nickel side leg 23 of connector 22 is joined, as by welding, to one of the conductors lb of the stem as shown in Fig. 4.

To aluminize the stem 14, said stem is first cleaned and dried to remove dirt and dust and surface alkalis on the glass which might impair the coating. The stem is then baked above C'. to remove water vapor from the glass- A suitable shield, such as a wide rubber band, may be positioned along the sealing edge of the flare l5 of stem l4. Said stem is then mounted within a suitable vacuum. bottle between four flashing fi1aments (not shown) which are appropriately arranged so that condensation of the vaporized metal occurs uniformly over the entire unshielded outside surface of the stem. The metal to be evaporated, in this case aluminum, may be placed on the flashing filaments in the form of U- shaped shavings or crimped aluminum ribbon. After the bottle has been evacuated, the filaments are heated quickly by the application of an appropriate. voltage. thus vaporizing, the: aluminum from the filaments and onto the. entire unshielded outside surface of the stem.

Th aluminum coating doesnot electricallyshort the leading-in conductors it because inconventional fluorescent lamps the Dumet sealing portion of said conductors does not extend to the top of press H3. The weld knot between the Dumet portion and the nickel portion of said conductor I6 is buried in the press. The nickel portion, not being wet by the glass, forms a crater 24, as shown in 3', extending from. the weld knot to the top of the press. The aluminum coat ing does not bridge this gap between the press glass and the nicket portion of the conductor;

In Fig. 6, is shown an alternative method of electrically connecting the aluminum coating to a modified. leading-in conductor it By extending the length of the Dumet portion of one of the conductors 16 such that the weld knot between the Dumet and the nickel portion is out of the press, a conductor such as. it of Fig. 6 is formed. In the case of conductor 16* a cavity 24 such as is formed about the other and conventional conductor It is not produced and the stem glass wets the. conductor throughout its length in thepress [8. When the stem- Me of Fig. 6 is aluminized, the uniform light reflecting film of aluminum 2! makes electrical connection with conductor l5- but not with conductor it.

If polarization of the anode of the fluorescent lamp is. desired, the coating may be split, suitably byproper shielding means prior to coating, or by scribing the coated surface into two handily symmetrical sections insulated from each other by moved, and the filamentary electrodes I? are mounted on the aluminized stems to form mounts l3. Said mounts are sealed into the envelope l0, and the lamp is exhausted and based as explained above.

Thus, it. is seen from the foregoing description that a preferred embodiment of my invention achieves a metallized stem for a low pressure gaseous discharge tube. or lamp. The metal coating on. said stem serves both as additional. anode area and as areflector of ultra-violetand/or visible: radiation. It will be understood, however,

that the functions of providing additional anode area and reflectivity need not be combined. A metal stem coating may serve as a reflector without electrical contact being made to an electrode and, as such, it is not restricted to use in gas discharge light sources, but may be employed in any luminescent device having a suitable stem, such as an incandescent lamp. Also for the purpose of increased anode area, an electrically conductive coating which need not be metallic or suitably reflective, may be applied to the stem and electrically connected to the electrode.

It will be further understood that the electrically conductive and/or light reflective coating may be applied to the stem by means other than evaporation, such as by the use of suitable paints. Also, a metallic sheath, suitably, .905" or less thick, having a configuration similar to that of the stem might be fitted over said stem.

Although embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

I claim:

1. A fluorescent lamp having a phosphor coated envelope, an ionizable medium within said en- 2r velope, a stem in each end of said envelope, said stem comprising a flare and a plurality of leading-in conductors sealed thereto by means of a press, each of said flares having a light reflecting and electrically conducting metallic anode film on its interior surface extending inwardly from a seal between said flare and said envelope, said film being in electrical contact with one of said conductors and serving as an anode during operation of said lamp and a filamentary cathode electrode on said conductors.

2.-An electrode mount for a fluorescent lamp having a stem, said stem comprising a flare and a plurality of leading-in conductors sealed thereto by means of a press, said flare having a light reflecting and electrically conducting metallic anode film on the outer vitreous surface thereof, and extending outwardly from the portion of said flare to be sealed to an envelope, said film being in electrical contact with one of said conductors for use as an anode, and a filamentary cathode electrode on said conductors.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,175,888 Flory Oct. 10, 1939 2,182,732 Meyer Dec. 5, 1939 2,405,089 Craig July 30, 1946 2,488,751 Verbeek Nov. 22, 1949 

